Magnet means for correction of blue beam lateral deflection for color television receiver tubes



Y' E. LEMIKE 3302,04

MAGNET MEANS FOR CORRECTION OF BLUE BEAM LATERAL DEFLECTION FOR COLORTELEVISION RECEIVER TUBES Filed May 3, 1965 I N VENTOR. fYJGE'A/F [iMA PUnited States Patent G 3,302,049 MAGNET MEANS FOR CORRECTION OF BLUEBEAM LATERAL DEFLECTION FOR COLOR TELEVISION RECEIVER TUBES EugeneLemke, Indianapolis, Ind., assignor to Radio Corporation of America, acorporation of Delaware Filed May 3, 1963, Ser. No. 277,800 4 Claims.(Cl. 313-75) The present invention relates to color televisionreceivers. More particularly the present invention relates to a bluelateral deflection arrangement for a multi-beam cathode ray tube of acolor television receiver.

Many color television receivers today utilize shadow mask color cathoderay tubes. The shadow mask tube has three electron guns and the screenof the cathode ray tube is arranged in a pattern of red, blue and greenemitting phosphors. The electron beams from the three electron gunsimpinge respectively on only one of the red, green or blue phosphors.The three beams, hereinafter referred to as the red, green and bluebeams respectively, are made to converge at the shadow mask. Theparticular phosphor which each beam contacts depends on the angle thebeam makes with the shadow mask at the convergence point.

A number of different beam convergence arrangements have been tried tobring about the desired meeting of the three beams at a single point. Byadjusting the beams in a radial direction it has been found that theintersection of two (such as, for example, the red and green) beams atthe desired point can be accomplished. However, it is not alwayspossible to make the third (such as, for example, the blue) beamconverge at the intersection of the red and green beams by radiallyadjusting the blue beam. Therefore means have been provided for adjustngthe blue beam in a lateral direction which permits the intersection ofall three beams at a desired point.

One of the difficulties of the blue beam deflecting devices has beentheir rather large size. The convergence assembly is mounted exteriorlyof the neck of the cathode ray tube and is arranged close to the end ofthe tube. The blue lateral deflection magnet is generally the closestcomponent to the socket end of the tube and therefore, during servicingof the television receiver it may inadvertently be moved out ofadjustment when the back cover of the receiver is replaced. By using thepresent invention it is possible to have a very small blue beam lateraldeflection device positioned about the neck of the cathode ray tube toprevent inadvertent movement thereof and yet to permit accurate lateraladjustment of the blue beam for convergence purposes.

It is accordingly an object of the present invention to overcome thedisadvantages of blue lateral deflection devices used in colortelevision receivers today.

A second object of the present invention is to provide a blue lateraldeflection device for the cathode ray tube of a color televisionreceiver which is very small in size and yet permits accurateadjustment.

With the above objects in view the present invention contemplates a bluelateral deflection magnet arrangement for cathode ray tubes. The tubeincludes an envelope within which is mounted at least three electronguns one for each of the red, blue green beams, respectively. A pair ofinternal pole pieces made of magnetic material are arranged in the tubeenvelope spaced on opposite sides of the electron gun for the blue beam.A blue lateral deflecting member made of magnetic material is movablymounted exteriorly of the cathode ray tube envelope adjacent theinternal pole pieces. The blue lateral deflecting member provides amagnetic flux at least part of which extends into the interior of thetube envelope. The member is movable between a first position whereinsubstantially all of the magnetic flux produced thereby and extendinginto the tube envelope passes through only one of the pair of polepieces without affecting any of the beams produced by the electron gunsand at least a second position. In the second position, the magneticflux produced by the deflection member and reaching inside the tubeenvelope passes through the pair of pole pieces and affects only theblue beam.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation together with additional objects and advantages thereof willbest be understood from the following description of an illustrativeembodiment when read in connection with the accompanying drawings inwhich:

FIGURE 1 is a schematic diagram of the deflection portion of a colortelevision receiver partially in block form showing a sectional view ofa cathode ray tube utilizing the present invention;

FIGURE 2 is a schematic showing of a method of magnetizing a bluelateral deflection member constructed in accordance with the principlesof the present invention;

FIGURE 3 is a sectional view taken along the lines 33 of FIGURE 1showing the blue lateral deflection member in its central position; and

FIGURES 4 and 5 are similar to FIGURE 3 showing the blue lateraldeflection member in its two extreme positions on the cathode ray tube.

Referring to the drawings and more particularly to FIGURE 1, the cathoderay tube 10 has a glass cone portion 11 to which is attached a glassfaceplate 12. A ranged on the inner surface of faceplate 12 is aluminescent screen 13 made up of dots of phosphors respective lyproducing light of the different primary colors in which the image is tobe reproduced upon impingement thereon of respective electron beams.Spaced from the luminescent area 13 is an aperture mask 14 containing anaperture for each of the primary color clusters used. For example if theprimary colors are red, blue and green, each cluster would contain threephosphor dots respectively emitting red, blue and green light uponexcitation.

Sshown converging at an aperture of the shadow mask 14 are threeelectron beams 16, 1'7 and 18. In order to obtain an accuratereproduction of the televised image it is desirable to have the threeelectron beams all converge at one point at the centers of therespective apertures.

The electron beams are produced at the opposite end of the cathode raytube 10 in the neck portion 19. The neck 19 has a nonmagnetic envelope21 made of glass, for example. Arranged within the glass envelope arethree substantially similar electron guns for the cathode ray tube 10,one for each of the primary colors blue, red and green, respectively.The cathode for the electron beam, which is aimed at the blue emittingphosphor, is identified by the numeral 22 having an associated controlgrid 23, an accelerating electrode 24, a focussing electrode 26 and anultor (or final accelerating) electrode 27. Except for the blue lateraldeflect-ion member which will be described subsequently, the red andgreen electron guns are identical to the blue structure. There may alsobe a conductive coating inside the funnel or cone portion 11electrically connected to the ultor 27 and to the phoshpors 12, 13, 14.

The video signals to be reproduced as an image are applied from thevideo amplifier (not illustrated) to the control grid 23 by meansincluding a coupling capacitor 28. In order to avoid unnecessarilycomplicating the drawing the components of the television receiver whichneed not be described for an understanding of this invention have notbeen illustrated with the exception of the blocks 29 and 31, whichrepresent respectively the vertical and horizontal deflection wavegenerators for the beams in the cathode ray tube. The complete detailsof a color television receiver in which the present invention may beembodied is shown in Color Television Service Data-File 1962 No.T6published by RCA Sales Corporation, 600 North Sherman Drive,Indianapolis, 1, Indiana.

The outputs of generators 29 and 31 are applied respectively by means ofconductors 32 and 33 to the yoke 34 surrounding the neck of the cathoderay tube 10. The yoke 34 contains the conventional horizontal andvertical deflection coils to which the deflecting currents are appliedto produce the deflecting magnetic fields for the electron beams passingtherethrough.

Arranged about the neck of the cathode ray tube just behind the yoke 34with respect to the screen is the static and dynamic beam convergencemember 36. The purpose of member 36 is to deflect the electron beamspassing therethrough in differing amounts depending upon the point ofimpingement of the electron beams on the luminescent screen. Thiscorrects for any beam convergence errors that may be introduced due tosuch known factors as the flatness of the screen 13, for example, inaccordance with the principles disclosed in such patents as No.2,751,519 granted to A. \V. Friend on June 19, 1956.

As a general rule the assembly 36 includes both static and dynamicconvergence magnets in a known manner. The static convergence magnet isgenerally a small permanent magnet mounted exteriorly of the tubeenvelope close- 1y adjacent to the beam it is to control. A typicalstatic convergence magnet structure and arrangement on the cathode raytube is shown in FIGURES 8 and 13 of the reference Service Data-File1962 No. T6.

The dynamic convergence member generally includes an electromagnet foreach electron beam. These electromagnets are mounted externally of thetube neck and are supplied with energizing current that vary with thedifferent positions of the beams during the horizontal and verticalscanning periods. To increase the effectiveness of the electromagnetseach one usually is provided with a pair of pole pieces mounted onopposite sides of the associated beam on the inside of the tube neck. Astructure of this nature is shown in Patent No. 2,707,248 granted to H.C. Goodrich on April 26, 1955. These dynamic convergence electromagnetsare energized from the vertical and horizontal deflection wavegenerators 29 and 31 as, for example, shown in FIGURE 47 of thereference Service DataFile 1962 No. T6.

Also mounted exterior-1y of the neck portion 19 of the tube 10 is a bluelateral deflection magnet 37. This arrangement may best be seen inFIGURE 3. The magnet 37 is shown arranged in the central portion of, andatop, the glass envelope 21 and supported in a nonmagnetic holder 38which, together with the magnet 37, is urged against the enevolep 21 bymeans of a tension spring 39. The spring 39 and the holder 38 encirclethe neck 19 of the tube 10. It can be seen in FIGURE 3 that the bluefocussing electrode 26 is arranged between two radially spaced internalpole pieces 41 and 42 which are made of a magnetic material.

The magnetic member 37 is a rectangular parallelopiped which ispermanently magnetized, by an apparatus such as partially shown inFIGURE 2, to have a magnetization geometry with the north and southpoles at the opposite ends of the longitudinal dimension. This isindicated schematically in FIGURE 2 wherein only the north pole 35 andthe south pole 45 of the magnetizing magnet are shown. The poles 35 and45 may be the pole pieces of an electromagnet. To appreciate the actualsize of the member 37 one such magnet which was found to operatesatisfactorily was made of barium ferrite 0.4 long, 0.25" wide and0.125" thick. The magnetic member 37 is arranged as shown in FIGURE 3 toproduce a flux which cooperates with the internal pole pieces 41 and 42.

In operation, the accelerating potentials generally associated with thecathode ray tube of a color television receiver are applied to thecathode raytube 10 for generating electron beams in the electron gunstructures thereof and directing the same along their respective pathtowards the screen 13. The video signals applied through couplingcondenser 28 vary the intensity of the respective electron beams and thebeams are deflected across the face of the screen 13 in synchronism withthe transmitted image by the magnetic fields set up by the deflectionyoke 34.

In the original installation of the cathode ray tube in the televisionreceiver and possibly in subsequent servicing the static convergencemagnets contained in the assembly 36 are generally moved radiallytowards and away from the aixs of the cathode ray tube to provide radialmovement of the beam affected by its respective magnetic field. In thismanner the red and green beams are caused to converge at the properaperture of the shadow mask. If the blue beam also converges at the samepoint the blue lateral deflection magnet 37 may remain in the centralposition illustrated in FIGURE 3.

In this position it may be seen that substantially all of the fluxentering the envelope 21 indicated by the lines 40 will be prevented bythe pole piece 41 from reaching the path of the electron beam passingthrough the electrode 26. That is, substantially all of such magneticflux flows from the north pole of the member 37 in the direction of thearrows through the pole piece 41 back to the south pole of member 37.Therefore the blue beam is not affected by the magnetic field set up bymagnetic member 37.

In the event it is found that lateral adjustment of the blue beam isnecessary or desirable, the member 37 may be moved through anyintermediate position to either of the extreme positions shown inFIGURES 4 and 5.

In FIGURE 4, the magnetic member 37 has been moved to its extremecounterclockwise position. It can be seen that in this position themagnetic flux entering the envelope 21 of the cathode ray tube will flowfrom the north pole of member 37 through the internal pole piece 42 andupwardly in the direction of the arrows to the pole piece 41, back tothe south pole of member 37.

In FIGURE 4 the electron beam for exciting the blue phosphor passesthrough the electrode 26 in a direction perpendicular to the plane ofthe drawing coming out of the drawing. The lines of magnetic flux 46 areshown to be substantially perpendicular to the path of movement of theblue electron beam. Therefore, the blue beam will be deflected to theleft in the direction of the arrow 47. How much the beam is deflectedwill of course depend upon the intensity of the magnetic field and thevelocity of the electrons passing therethrough. The intensity of themagnetic field may be adjusted even though the lines of flux are stillmaintained in the illustrated direction by moving the magnetic member 37between its central position shown in FIGURE 3 and its counterclockwiseextreme position shown in FIGURE 4.

Similarly in FIGURE 5 the magnetic member 37 is shown moved to itsextreme clockwise position. The resulting lines of flux are directed outof phase with the arrangement shown in FIGURE 4 but are stillperpendicular to the path of the electron beam passing through theelectrode 36. The electron beam will therefore be laterally deflected tothe right in the direction of the arrow 48. As before, differentintensity fields may be obtained by shifting the member 37 between thecentral position and the clockwise extreme position shown in FIGURE 5.

In the central position of FIGURE 3 and the two extreme positions ofFIGURES 4 and 5, as well as all the intermediate positions,substantially none of the lines of flux entering the envelope 21 areable to affect the electron beams'passing through the red or green beamfocussing electrodes 51 and 52 respectively. That is, the pole pieces 41and 42 cooperate to prevent any of the magnetic flux produced by themagnetic member 37 from affecting the electron beams which are not to belaterally displaced.

By use of the magnetic member 37 in cooperation with the internal polepieces 41 and 42 it is possible to deflect the electron beam used forexcitation of the blue phosphor laterally in either direction by varyingamounts. It has been found for example that with the illustratedarrangement it is possible to obtain a total beam deflection on the faceof a 70 color kinescope of $0.4. This is generally sufficient to meetmost such color kinescope requirements.

If desired, of course, an arrangement such as has been described for theblue beam may be used for the red or green beams to produce the properintersection of the three beams.

It can also be seen that, because of the relatively small size of themagnetic member 37, it is possible to prevent, or at least minimize,inadvertent movement of this device due to the removal and replacementof the socket of the cathode ray tube and the manipulation of otherapparatus such as the static convergence magnets, for example, duringservicing of the color television receiver.

What is claimed is:

1. For use in a color television receiver, in combination,

a cathode ray tube having an envelope, a screen and a neck portion, atleast part of said neck portion being made of a nonmagnetic material,said cathode ray tube further including at least three electron gunsmounted within said neck portion, each of said electron gunsrespectively emitting an electron beam along a path towards said screen;

a pair of substantially parallel internal pole pieces made of magneticmaterial and arranged transversely within said tube envelope on oppositesides of one of said electron guns;

a nonmagnetic holder mounted exteriorly of said nonmagnetic neck portionof said envelope adjacent said pole pieces and movable circumferentiallyabout said neck portion; and

a lateral beam deflecting member made of magnetic material mounted insaid nonmagnetic holder for producing a magnetic flux extending intosaid cathode ray tube envelope, said nonmagnetic holder bein movableinto a first circumferential position in which said lateral beamdeflecting member is substantially parallel to said pole pieces whereinsubstantially all of the magnetic flux emitted thereby and extendinginto said tube envelope passes through only one of said pair of polepieces and does not extend into the path of any of the electron beamsand being further movable to at least a second circumferential positionwherein said magnetic flux extending into said tube envelope passesthrough both of said internal pole pieces and into the path of only saidelectron beam emitted by said one of said electron guns.

2. For use in a color television receiver, in combination,

a cathode ray tube having an envelope, a screen and a neck portion, atleast part of said neck portion being made of a nonmagnetic material,said cathode ray tube further including at least three electron gunsmounted within said neck portion, each of said electron gunsrespectively emitting an electron beam alon" a path towards said screenthereof;

a pair of substantially parallel internal pole pieces made of magneticmaterial and arranged transversely within said tube envelope on oppositesides of one of said electron guns so as to effectively isolatemagnetically the electron beam produced by said one electron gun fromthe electron beams produced by the others of said electron guns;

a nonmagnetic holder mounted exteriorly of said nonmagnetic neck portionof said envelope adjacent said pole pieces and movable circumferentiallyabout said neck portion; and

a lateral beam deflecting member made of magnetic material mounted insaid nonmagnetic holder for producing a magnetic flux extending intosaid oath ode ray tube envelope, said nonmagnetic holder being movablebetween a first circumferential position in which said lateral beamdeflecting member is substantially parallel to said pole pieces and atleast two extreme non-parallel circumferential positions whereby in saidfirst circumferential position substantially all of said magnetic fluxextending into said tube envelope passes through only one of said pairof pole pieces and does not intersect the paths of any of said electronbeams and in each of said two extreme circumferential positions, saidmagnetic flux passes through both of said internal pole pieces andintersects the path of only one of said electron beams.

3-. Apparatus as claimed in claim 2 wherein the direction of themagnetic fiux intersecting said path of said electron beam in one ofsaid extreme circumferential positions is opposite to the direction ofthe magnetic flux intersecting said electron beam path in the other ofsaid extreme circumferential positions.

4. In a blue lateral beam deflecting arrangement for cathode ray tubesused in a color television receiver wherein the cathode ray tube has atleast three electron guns respectively emitting red, blue and greenphosphor exciting electron beams, the improvement comprising, a pair ofinternal pole pieces made of magnetic material and mounted on oppositesides of the electron gun producing the blue phosphor exciting beam, oneof said pole pieces being radially outwardly of said blue beam producingelectron gun and the other of said pole pieces being disposed radiallyinwardly of said blue beam producing electron gun;

a nonmagnetic holder mounted exteriorly of said nonmagnetic neck portionof said envelope adjacent said pole pieces and movable circumferentiallyabout said neck portion; and

a rectangular parallelopiped blue lateral beam-deflecting member havingits longest dimension smaller than the diameter of the neck portion ofthe cathode ray tube, said member being made of magnetic material andmounted in said nonmagnetic holder, said member being magnetized toproduce magnetic flux extending into the neck portion of the cathode raytube, said nonmagnetic holder being movable between a firstcircumferential position in which said lateral beam deflecting member issubstantially parallel to said pole pieces wherein substantially all ofthe magnetic flux produced by said lateral beam deflecting member andextending into the neck portion of the cathode ray tube cooperates withand passes through one of said pair of pole pieces without affecting thedirection of movement of the red, blue or green phosphor excitingelectron beams, said nonmagnetic holder being movable into at least asecond circumferential position wherein substantially all of themagnetic flux produced by said lateral beam deflecting member andextending into the neck portion of the cathode ray tube passes throughboth of said pair of pole pieces and affects the path of movement ofonly the blue one of said red, blue or green phosphor exciting electronbeams.

References Cited by the Examiner UNITED STATES PATENTS 2,752,520 6/1956Morrell 3 l3-70 2,769,110 10/1956 Obert 313 2,806,164 9/1957 Clay et al.3l3--75 3,192,452 6/1965 Rennick 317-200 JAMES W. LAWRENCE, PrimaryExaminer.

V. LA FRANCHI, Assistant Examiner.

1. FOR USE IN A COLOR TELEVISION RECEIVER, IN COMBINATION, A CATHODE RAYTUBE HAVING AN ENVELOPE, A SCREEN AND A NECK PORTION, AT LEAST PART OFSAID NECK PORTION BEING MADE OF A NONMAGNETIC MATERIAL, SAID CATHODE RAYTUBE FURTHER INCLUDING AT LEAST THREE ELECTRON GUNS MOUNTED WITHIN SAIDNECK PORTION, EACH OF SAID ELECTRON GUNS RESPECTIVELY EMITTING ANELECTRON BEAM ALONG A PATH TOWARDS SAID SCREEN; A PAIR OF SUBSTANTIALLYPARALLEL INTERNAL POLE PIECES MADE OF MAGNETIC MATERIAL AND ARRANGEDTRANSVERSELY WITHIN SAID TUBE ENVELOPE ON OPPOSITE SIDES OF ONE OF SAIDELECTRON GUNS; A NONMAGNETIC HOLDER MOUNTED EXTERIORLY OF SAIDNONMAGNETIC NECK PORTION OF SAID ENVELOPE ADJACENT SAID POLE PIECES ANDMOVABLE CIRCUMFERENTIALLY ABOUT SAID NECK PORTION; AND A LATERAL BEAMDEFLECTING MEMBER MADE OF MAGNETIC MATERIAL MOUNTED IN SAID NONMAGNETICHOLDER FOR PRODUCING A MAGNETIC FLUX EXTENDING INTO SAID CATHODE RAYTUBE ENVELOPE, SAID NONMAGNETIC HOLDER BEING MOVABLE INTO A FIRSTCIRCUMFERENTIAL POSITION IN WHICH SAID LATERAL BEAM DEFLECTING MEMBER ISSUBSTANTIALLY PARALLEL TO SAID POLE PIECES WHEREIN SUBSTANTIALLY ALL OFTHE MAGNETIC FLUX EMITTED THEREBY AND EXTENDING INTO SAID TUBE ENVELOPEPASSES THROUGH ONLY ONE OF SAID PAIR OF POLE PIECES AND DOES NOT EXTENDINTO THE PATH OF ANY OF THE ELECTRON BEAMS AND BEING FURTHER MOVABLE TOAT LEAST A SECOND CIRCUMFERENTIAL POSITION WHEREIN SAID MAGNETIC FLUXEXTENDING INTO SAID TUBE ENVELOPE PASSES THROUGH BOTH OF SAID INTERNALPOLE PIECES AND INTO THE PATH OF ONLY SAID ELECTRON BEAM EMITTED BY SAIDONE OF SAID ELECTRON GUNS.